The graph above shows completion of the main story quests; as a bar
chart (on Jan 17) and as a time series in days since release. Unbound
is 100% because the statistics only count players who’ve completed
one achievement. There’s a big falloff after “The Way of the
Voice”; only 57% of players started Act II of the game. And 34%
of players finished the game after two months; most players who get as
far as Elder Knowledge in Act III complete the whole game.

I’ve made graphs
for all 50 achievements. The bar charts show which parts of the game
are popular. For instance 74% of players joined the Companions compared
to only 45% joining the Dark Brotherhood. I suspect that’s
mostly due to game structure; it’s hard to avoid meeting
the Companions at Whiterun but the player has to actively seek out
the Dark Brotherhood. Faction completion is also interesting; mages
complete their faction line the most while precious few people finish
the Thieves Guild. Only ⅓ of players got married; I think the option
may have been too hidden. I’m impressed 12% of players got Oblivion Walker;
it takes a significant commitment to get 15 Daedric Artifacts and if
the player screws up they can make it impossible.

Unfortunately the time series graphs don’t give a lot of
extra insight. There’s a big dip in completion percentages around
Christmas, when a bunch of new players started playing. But the basic
velocity of completion, the slope of these graphs, is about the same
for all of the achievements. In retrospect that’s not surprising
but I was hoping it would be more interesting.

Some caveats about the data. It’s Xbox
only, a self-selected subset of players that True
Achievements tracks. The data is daily and has a few bad days I
fudged out. This graph isn’t really a finished work, but honestly
the data didn’t turn out to be very interesting so I’m done
with it.

Update: you can
see bar charts of PC achievement completion on
Steam. To compare to Xbox, normalize PC numbers to who
completed Unbound (92.4%) and look at
current Xbox data.
Fewer people have finished the main quest on PC (31%) vs Xbox (40%).
And only 2.5% of PC users have completed Oblivion Walker, compare to
15% on Xbox. Far fewer finished the thieves guild, too (7% vs 21%).
Maybe PC players aren't as completionist as Xbox players? It's not just
time played;
63% of people hit Level 25 on PC, 68% on Xbox, that's pretty close.
Maybe it's the Xbox sample bias; TrueAchievements tends to track players who
are worried about completing achievements.